How to get checkbox value from a TGroupBox in Delphi?

I have a groupbox and three check boxes in a form. And I want to get the user selected values in an array of values and If he doesn't selects one then the default enabled checkbox value needs to be selected into an array.

var selectedValues:String;
selectedValues:= getSelectedCheckboxValue(); //Here I want to pass the  selected values to store it into an array
function getSelectedCheckboxValue(): string;
begin
 var retArr:array[1..3] of string;
 return retArr;
end;

Is my approach correct? Or Is there an other way to do it.